The present invention relates to constant velocity fixed universal joints and, in particular, concerns a constant velocity fixed joint of the type comprising: (1) an outer joint member of hollow configuration, having a rotational axis and in its interior, a plurality of arcuate tracks circumferentially spaced about the axis extending in meridian planes relative to the axis, and forming lands between the tracks and integral with the outer joint part wherein the lands have radially inwardly directed surfaces; (2) an inner joint member disposed within the outer joint member and having a rotational axis, the inner joint member having on its exterior a plurality of tracks whose centerline lie in meridian planes with respect to the rotational axis of the inner joint member in which face the tracks of the outer joint member and opposed pairs, wherein lands are defined between the tracks on the inner joint member and have radially outwardly directed surfaces; (3) a plurality of balls disposed one in each pair of facing tracks in the outer and inner joint members for torque transmission between the members; and (4) a cage of annular configuration disposed between the joint members and having openings in which respective balls are received and constrained so that their centers lie in a common plane, wherein the cage has external and internal surfaces each of which cooperate with the land surfaces of the outer joint member and inner joint member, respectively, to locate the cage and the inner joint member axially.
In joints of this kind, the configuration of the tracks in the inner and outer joint members, and/or the internal and external surfaces of the cage are such that, when the joint is articulated, the common plane containing the centers of the balls substantially bisects the angle between the rotational axes of the joint members.
There are several types of joint of the kind specified differing from one another, inter alia, with respect to the arrangement and configuration of the tracks in the joint members and/or to the internal and external surfaces of the cage whereby the common bisector plane is guided as described above thereby giving the joint constant-velocity-ratio operating characteristics. What such different types of joints have in common, however, is that the cage is located axially in the joint by cooperation between the external cage surface and the surfaces of the lands facing the cage surface.
The outer surface of the cage and cooperating land surfaces of the outer joint member are generally spherical. When torque is transmitted by the joint, the forces acting in the joint cause the cage to be urged towards one end of the joint (i.e. ball expulsion forces); which end will depend on the respective directions of the offsets of the tracks in the inner and outer joint members from the common plane when the joint is in its unarticulated position To reduce the normal forces acting on the cage as a result of these ball expulsion forces, the amount of spherical wrap by the outer joint member lands should be maximized for increased cage support. However, the more the outer joint part lands spherically enclose the spherical outer surface of the cage, the more difficult the introduction of the ball cage into the outer joint part becomes. In a disc-style constant velocity fixed joint wherein the outer joint member is open on both ends, the cage is assembled from the end opposite the end towards which the cage is urged by ball expulsion forces under articulated load conditions. Assembly of the cage into the outer joint member is typically accomplished by either incorporating cage assembly notches into one of or a pair of lands in the outer joint member, or by sufficiently increasing the bore diameter of the outer joint part to allow the ball cage to be introduced into the outer joint part.
In a mono-block constant velocity fixed joint wherein the outer joint part is a bell-shaped member having a closed end, the cage must be assembled from the open end of the outer joint member. To accommodate assembly of the cage into the outer joint part, again, the bore diameter of the outer joint part must be sufficiently increased to allow assembly and/or assembly notches must be incorporated into at least one opposing pair of the outer joint member lands to allow introduction of the cage. Either method is undesirable however in that both assembly methods reduce the amount of spherical wrap available for cage support. In turn, higher surface stresses are induced to the cooperating surfaces of the outer joint part and the cage resulting in greater heat generation due to increased friction.
Accordingly, it is an object of the present invention to provide a constant velocity fixed joint with an improved cage assembly. According to the present invention, the foregoing and other objects are obtained by a fixed constant-velocity-ratio universal joint, comprising an outer joint part, an inner joint part, a ball cage and a plurality of balls. The outer joint part has a hollow configuration and includes a rotational axis, a plurality of at least partially arcuate tracks circumferentially spaced about the axis in the interior of the outer joint part and having center lines extending in meridian planes relative to the axis, and lands defined between the tracks and which are integral with the outer joint part and have inwardly directed surfaces. The inner joint part is disposed within the outer joint part and includes a rotational axis, a plurality of at least partially arcuate tracks on the exterior of the inner joint part having center lines extending in meridian planes with respect to the rotational axis of the inner joint part and which faces the tracks in the outer joint part in opposed pairs, and lands defined between the tracks on the inner joint part having radially-outwardly directed surfaces. The plurality of balls are disposed one in each pair of facing tracks in the outer and inner joint parts for torque transmission between the parts. The ball cage is disposed between the inner and outer joint parts and includes windows in which respective balls are received and constrained such that their centers lie in a common plane. At least two opposing windows are wider than the outer joint part lands to accommodate receiving the lands during assembly. The cage includes substantially spherical inner and outer surfaces which engage the land surfaces on the inner and outer joint parts respectively.
The ball cage also includes a relief groove between at least one pair of adjacent windows thereby providing a reduced circumference for the ball cage outer surface in the region of the groove. The groove is at least as wide as one of the outer joint part lands to accommodate introduction of the ball cage into the outer joint part when the ball cage is rotated about a transverse axis by 90xc2x0 with respect to the outer joint part axis. In one aspect of the invention, the groove is an annular groove about the circumference of the cage outer surface. In another aspect of the invention, the groove comprises two grooves centered about the central ball plane of the cage and corresponding to the outer joint part land width.
One advantage of the present invention is that it maximizes the spherical wrap of the outer joint member lands with respect to the outer surface of the cage. Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.